In a large bowl, combine the yeast and flour; add butter and mix well. Add egg yolks and sour cream; mix well. Shape into four balls. Place in separate resealable plastic bags or wrap in plastic; refrigerate overnight. , Combine sugar, pecans and cinnamon; set aside. On a floured surface, roll each ball of dough into a 9-in. circle. Sprinkle with sugar mixture and apple. Cut each circle into 16 wedges; roll up from wide edge and pinch to seal. Place with point side down on greased baking sheets. , Bake at 350° for 16-20 minutes or until lightly browned. Immediately remove to wire racks to cool. For icing, combine sugar, milk and vanilla until smooth; drizzle over the twists. Sprinkle with pecans.